1. Field of the Invention
The present invention relates to a grism, and more particularly to a grism used suitably for a variety of apparatuses in observation for astronomy, earth and planetary science, meteorology, environmental hygienics and the like; various spectroscopic analyzer for physics and chemistry, pathology or the like and applied to mineral substances, living organisms or the like; manufacturing installations and quality control systems for foodstuffs, medicines, chemical products or the like; and all-optical routing apparatus relating to bare bones of Wavelength Division Multiplexing (WDM) in optical communication.
It is to be noted herein that “grism” is a transmission type dispersive element prepared by combining a prism or prisms with a transmission grating so as to allow a light beam having an arbitrary order and an arbitrary wavelength to go straight or in an arbitrary direction.
2. Description of the Related Art
In recent years, a number of apparatuses for observation having both functions of imaging function and spectroscopic function have been developed with progress of two-dimensional detectors in fields of astronomy, earth and planetary science, meteorology, and environmental hygienics. In such an apparatus for observation, a grism is frequently used for a dispersive element.
Since a vertex angle of a prism constituting a grism is fixed in a conventional grism, rectilinear propagating wavelength and most effective wavelength have been fixed also.
For this reason, there has been such a problem that a plurality of grisms having different rectilinear propagating wavelengths must be prepared in the case where highly dispersive spectroscopy is conducted in wide wavelength.